1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, a thin film etching method and a method of fabricating a liquid crystal display device using the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for process simplification and manufacturing cost reduction of thin films.
2. Discussion of the Related Art
As the information-oriented society is developing, the demands for display devices gradually rise. Many efforts have been made to research and develop various flat panel display devices, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescent display (ELD) devices and vacuum fluorescent display (VFD). Among the various types of flat display devices, LCD devices have been most widely used as a substitute for a cathode ray tube (CRT) devices due their advantageous characteristics of thin profile, light weight, and low power consumption. For example, LCD devices have been used in car-mounted monitors, color televisions, laptop computers and pocket computers.
To make LCD devices usable in various fields as a general display device, LCD devices need to implement an image of high quality including high definition, high luminance, wide area and the like while maintaining the characteristics of lightweight, slim size and low power consumption. In general, an LCD device includes a liquid crystal display panel displaying an image thereon and a drive unit for applying a drive signal to the liquid crystal display panel. The liquid crystal display panel includes a first glass substrate, a second glass substrate, and a liquid crystal layer between the first and second glass substrates.
The first glass substrate, which is often referred to as a TFT array substrate, includes a plurality of gate lines arranged in one direction, a plurality of data lines arranged in a direction perpendicular to the gate lines, a plurality of pixel electrodes arranged in a matrix form on a plurality of pixel areas defined by crossings between the gate and data lines, and a plurality of thin film transistors in the pixel areas to selectively deliver signals of the data lines to the pixel electrodes. The second glass substrate, which is often referred to as a color filter substrate, includes a black matrix layer to block light from an area excluding the pixel areas, an R/G/B color filter layer to represent colors, and a common electrode to implement an image.
The first and second glass substrates are bonded together by a sealant with a space therebetween maintained by spacers. A liquid crystal inlet is initially formed in the sealant, such that a liquid crystal material is injected between the bonded first and second glass substrates through the liquid crystal inlet. For example, by submerging the liquid crystal inlet in a container holding the liquid crystal material under a vacuum state, the liquid crystal material is injected between the bonded first and second glass substrates by osmosis. After the liquid crystal material is injected, the liquid crystal inlet is then sealed.
In a general fabricating process of an integrated circuit, transistor, LCD, diode and the like, a photolithography process for forming a micro pattern and an etching process through the micro pattern are used to form a thin film pattern. The photolithography process includes coating a resist material, exposure the coated resist material through a photomask and development of the exposed resist material to form the micro pattern.
FIGS. 1A to 1C are cross-sectional views illustrating a thin film etching method according to the related art. An object etching method and a liquid crystal display device fabricating method using the same according to the related art are explained with reference to the attached drawings as follows. Referring to FIG. 1A, a substrate 1 includes an insulating layer 2, a metal layer 3, and a photoresist layer 4 sequentially formed thereon. The photoresist layer 4 can be formed by one of spin coating process, spray coating process, and deep coating process. In particular, spin coating by rotating a substrate, which is held by a chuck, at high speed in a vacuum state is commonly used due to its good stability and uniformity. In addition, a photomask 5 having a specific pattern shape is placed over the substrate 1 having the photoresist layer 4. Then, UV-rays (shown as arrows) are irradiated the substrate 1 through the photomask 5 for exposure.
Referring to FIG. 1B, the exposure-treated photoresist layer 4 (shown in FIG. 1A) is developed into a photoresist pattern 4a corresponding to the specific pattern shape of the photomask 5. In developing the exposure-treated photoresist layer 4, deposition or spray is used. In the deposition development method, it is difficult to manage temperature, concentration, aging effect and the like. In comparison, the spray development method is more advantageous in managing temperature, concentration, aging effect and the like. Thus, in general, an in-line instrument employing the spray development method is used. Subsequently, the metal layer 3 (shown in FIG. 1A) is selectively removed by a dry or wet etching process using the photoresist pattern 4a as an etch mask to form a metal line 3a. 
Referring to FIG. 1C, the photoresist pattern 4a (shown in FIG. 1B) used as the etch mask in forming the metal line 3a is removed. The photoresist pattern 4a can be removed by using O2 plasma or various oxidizers. For example, in the O2 plasma method, O2 gas is injected with a high voltage in a vacuum state to generate O2 plasma, such that the O2 plasma reacts with a photoresist to dissolve and remove the photoresist. However, such a method needs expensive equipment to generate the O2 plasma, and rotational particles in the O2 plasma cause undesired damage to a substrate. In the method using oxidizers, thermal concentric sulfuric acid or a mixed solution of thermal concentric sulfuric acid and hydro peroxide is used as an oxidizer. Thus, in fabricating a liquid crystal display device, coating, exposure and development processes are repeatedly carried out to form various photoresist patterns as etching masks, and the process of removing the photoresist patterns is repeated as well. Thus, the fabrication process is time consuming and expensive.
FIGS. 2A to 2F are cross-sectional views illustrating a method of fabricating a liquid crystal display device according to the related art. Referring to FIG. 2A, a metal layer is formed on a transparent first substrate 11 and a first photoresist layer (not shown) is coated on the deposited metal layer. Exposure and development processes are carried out on the first photoresist to selectively form a first photoresist pattern. Subsequently, the metal layer is selectively removed using the first photoresist pattern as a first etch mask to form a gate electrode 12 and a gate line (not shown) extending from the gate electrode 12 in a first direction. Then, the first photoresist pattern is removed.
An insulating material, such as silicon nitride or silicon oxide, is deposited on the first substrate 11 including the gate electrode 12 to form a gate insulating layer 13. An amorphous silicon layer and a doped amorphous silicon layer are sequentially formed on the gate insulating layer 13. After a second photoresist layer has been coated on the doped amorphous silicon layer, the second photoresist layer is patterned by exposure and development processes to form a second photoresist pattern. Subsequently, the doped amorphous silicon layer and the amorphous silicon layer are selectively removed using the second photoresist pattern as a second etch mask to form an active layer 14 and an ohmic contact layer 15. Then, the second photoresist pattern is removed.
Referring to FIG. 2B, a second metal layer is formed on the first substrate 11, a third photoresist layer is coated on the second metal layer, and a third photoresist pattern is then formed by patterning the third photoresist layer using exposure and development processes. The second metal layer is selectively removed using the third photoresist pattern as a third etch mask to form a source electrode 16a and a drain electrode 16b at lateral ends on the active layer 14. Although not shown, the source electrode 16a extends from a data line, which vertically crosses the gate line, to thereby define a pixel area. In particular, the source and rain electrodes 16a and 16b are spaced apart from each other to form a channel in a later process. Thus, a portion of the ohmic contact layer 15 is exposed between the source and drain electrodes 16a and 16b. The source and drain electrodes 16a and 16b together with the gate electrode 12 form a thin film transistor T. Then, the third photoresist pattern is removed.
Referring to FIG. 2C, a silicon oxide, silicon nitride or organic insulating layer is formed on the source and drain electrodes 16a and 16b to form a protecting layer 17. When forming the protecting layer 17 with the organic insulating layer, no step difference is created by the thin film transistor T because the organic insulating layer can be formed to be planar. In addition, a fourth photoresist layer is coated on the protecting layer 17 and is then patterned by exposure and development processes to form a fourth photoresist pattern. A contact hole 18 is formed by selectively removing a portion of the protecting layer 17 to expose a predetermined surface of the drain electrode 16b using the fourth photoresist pattern as a fourth etch mask. Then, the fourth photoresist pattern is removed.
Referring to FIG. 2D, a transparent metal layer, such as an ITO layer, is formed on the first substrate 11 including the contact hole 18. A fifth photoresist layer is coated on the transparent metal layer and is then patterned by exposure and development processes to form a fifth photoresist pattern. Subsequently, a portion of the transparent metal layer is selectively removed using the fifth photoresist pattern as a fifth etch mask to form a pixel electrode 19 electrically connected to the drain electrode 16b via the contact hole 18. Then, the fifth photoresist pattern is removed.
Referring to FIG. 2E, a first alignment layer 20 is formed over the first substrate 11 including the pixel electrode 19. The first alignment layer 20 is formed by coating a polymer film and aligning the polymer film by a rubbing process. A polyimide-based organic substance is generally used as the alignment layer. The rubbing process, which includes the step of rubbing the alignment layer in a predetermined direction using a rubbing cloth, is suitable for mass production and provides a stable pretilt angle alignment. Recently, a photo alignment method using a polarized light is developed and used.
Referring to FIG. 2F, a second substrate 31 facing the first substrate 11. The second substrate 31 includes a black matrix 32. The black matrix 32 is a Cr layer or the like to prevent light leakage through areas of the second substrate 31 except for the pixel areas. The black matrix 32 is formed by a photolithography process. In addition, a color filter 33 is formed on the second substrate 31 between gaps of the black matrix 32. The color filter 33 includes red, green and blue sub-color filters, and each of the sub-colors corresponds to one pixel area.
A common electrode 34 is formed on the second substrate 31 including the color filter 33. Further, a second alignment layer 35 is formed of a material, such as polyimide and the like, on the common electrode 34 such that a surface of the second alignment layer 35 is oriented in a predetermined direction.
A seal pattern (not shown) is formed on one the first substrate 11 and the second substrate 31. The seal pattern is located at a periphery of a display area, includes a gap for liquid crystal injection and prevents leakage of the injected liquid crystals. The seal pattern is formed using a thermo-hardening resin by a screen print method using a screen mask or a seal dispenser method using a dispenser.
To simplify the process, the screen print method is widely used. However, it is difficult for using the screen mask with a large-sized substrate. In addition, the screen print method induces failure due to the contact between the mask and the alignment layer. Thus, the screen print method tends to be replaced by the seal dispenser method.
To keep the uniform gap between the first and second substrates 11 and 31, spacers (not shown) are scattered on one the first substrate 11 and the second substrate 31. The spacers are scattered by wet scattering of a mixture of spacers and alcohol and the like or dry scattering of spacers only. Dry scattering is divided into electrostatic scattering using static electricity and non-electric scattering using a gas pressure. Since the liquid crystal display device is vulnerable to static electricity, non-electric scattering is widely used.
Subsequently, the first and second substrates 11 and 31 are loaded in a bonding chamber and are bonded to each other by pressurizing and hardening the seal pattern. As a result, the first substrate 11 and the second substrate 31 are arranged with the first and second alignment layers 20 and 35 facing each other and the pixel electrode 19 facing the color filter 33 in one-to-one manner.
After the first and second substrates 11 and 31 are bonded to each other, a liquid crystal material is injected between the bonded first and second substrates 11 and 31 via the gap in the seal pattern to form a liquid crystal layer 40. The liquid crystal injection is carried out by vacuum injection using a difference between inner and outer pressures of the LCD panel. When the liquid crystal molecules are injected in the LCD panel, air amongst the liquid crystal molecules creates bubbles within the LCD panel that cause device failure. To prevent the bubble generation, a process of removing the bubbles by leaving the liquid crystal molecules in a vacuum state for a considerable time is needed. After completion of the liquid crystal injection, the gap in the seal pattern is sealed to prevent the liquid crystal material from flowing out via the gap.
The related art thin film etching method and method of fabricating a liquid crystal display device using the same have the following problems. First, the photoresist layer has to be formed on the object layer to be etched, such as an insulating layer, a semiconductor layer or a metal layer. Then, exposure and development processes are carried out to pattern the photoresist layer through a photomask. Subsequently, the object layer can be selectively etching using the patterned photoresist layer as an etch mask. Then, the photoresist is removed. Accordingly, the related art method repeats the above steps, thereby complicating the fabrication process and lowering productivity.